Method of forming sheet metal



` March 5, 1946'. H. M. JAG'ER ET Al.

METHOD OF lF'ORMING SHEET METAL original Filed Nov. s, 1942 A mvENToRs:

Edouard @chen/f. BY Howard M daje/'f A'rr'm.

Patented Mar. 5, 1946 1- METHOD OF FORMINGISHEET METAL Howard M. Jager, Oceanside, and Edouard Schenk, New York, N. Y., assignors to Republic a corporation of Dela- Aviation Corporation, ware Original application November 3, 1942, Serial No. 464,356. Divided and this application June 30,l

1943, Serial No. 492,796

lt claims.

The present invention has to do with forming sheet metal into various hollow shapes, and this application is a division of our application bearing Serial No. 464,356, and filed November 3, 1942.

'I'his method proposes the formation of hollow bodies from metallic sheets and is especially concerned with the fixed and clamping engagement of opposed edges of the sheet kto be formed against slippage or disengagement during the shaping and forming of the body thereof between such edges and to that end so shapes, engages and manipulates the edges of the sheet that the force or forces required to fixedly and clampingly engage said edges at all timesexceeds the force employed in forming, stretching or shaping the body of the sheet between the engaged or clamping'edges. g

The instant method is such that a single clamping mechanism or means may be used for the engagement of the opposed edges of the sheet thereby bringing said edges into relatively close proximity during the forming or stretching of the sheet thus making possible the formation of hollow bodies constricted at both ends or edges, i. e. bodies tapering from a medial point or axis toward their ends or side edges such as the airfoils, iins, rudders, flaps, ailerons, elevators, stabilizers, etc. which constitute components of aircraft and have distinctive aerodynamic shapes which do not lend themselves readily to the presently recognized methods of sheet metal forming.

The other objects of, and results achieved by, the invention will become manifest as this disclosure proceeds.

One form of embodiment of the inventive concepts is shown in the accompanying drawing, and described hereinafter, by way of example, only; and it is to be understood that the invention is limited in its embodiments only by the scope of the subjoined claims.

In the drawing: Y

Figure 1 is a fragmentary side elevation of a sheet metal forming machine which may be employed in carrying out part of the present method;

Figure 2 is an enlarged end-view, partly in section, along line 2 2 of Figure 1; and

Figure 3 is an enlarged section along line 3-3 of Figure 1, showing the parts in another position.

The stretching machine is shown as applied to form the skin of the leading or hinge edge of an aircraft rudder and includes a stationary lower 55 form 'blockv 22, in the lower -portionof which. is

formed in a pair of H-shaped uprights 24 formi ing part of a support vor operating table 25, 26. Before it is processed therein, the metal sheet 20 to be formed is bent in a compound bend along its opposed longitudinal edges in such manner as to form two U-channelled retaining borders. It is then fitted overan upper movable formblock 2I of the machine, which block rests on the stationary block 22'.

The single clamp used to anchor the longitudinal channelled edges of the sheet 20 around legs 22 during' the stretching operation includes a gang nut or wedge I0, Vand a lower jaw II suspended from said wedge by means of a plurality of tightening devices.` The upper jaw of the clamp is formed by the legs 22 of the block 22, and both slanting sides of` thewedge I0, instead of but one side, cooperate with the inner faces ofy saidV legs 22' to clamp the upturned wings of the ,U-chan-r nels formed along the edges of the work sheet 20. In the present apparatus there are tightening devices Vin the form of studs I2, having opposed.

heads I3, I Il.A Through holesin the'lower heads I4 passes a longitudinal shaft I5 made in two parts, each part carrying a plurality of camsor eccentrics I6, Xed on the shaft I5 by means of keys I'I. The two halves of the shaft l5 may be operated simultaneously by means of a pair of opposed handles IS, slidably mounted across hubs I8 xed on the' opposed outer ends of the shaft parts I 5.

The upper movable block 2| can be spread apart from the lower block 22, with the sheet of metal engaged around the top, by means of a hydraulic jack schematically shown as a power unit tting within a corresponding 'elongated hole formed half in the block 2I and half in the block 22. This -power unit comprises an elongated hydraulic chamber 28 preferably of U- section housed in the fixed block 22 and an elongated plunger 29, the head of which is similarly housed in the movable block 2I. An operating fluid 30, preferably oil, is admitted into the chamber 28 through conduits (not shown).

Each clamping assembly, including elements III-I9, rests freely on the table 25, 2S when the machine isat rest (asin Figures 1 and 2) and is carried by the block 22 when the machine is in operation (as in Figure 3). Y

In order to facilitate the insertion of the channelled edges of the work sheet 2n around the legs 22', the table 25, 26 is extended considerably beyond the two ears 23 and the two clamping assemblies I to I9, can be slid in opposite directions along said extensions by means of cooperating slanting guiding surfaces 21, 3l vso as to clear the two lateralentrances for said channelled edges provided between each of the legs 22' and the corresponding longron 25 of the table 25., 26. Normally, there is no fluid in the chamber 28, and the movable block 2l rests upon the i'lxed block 22. When it is desired to put a work sheet 20 in position on the form 2 I, 22, the two clamping assemblies I0 to I9, are rst withdrawn from under the block 22 and one U-channel only of the work sheet 20 is engaged upwardly over one leg 22 of the block 22, the sheet being held vertically and then i'ltted over the top of the block 2I, and the opposite U-channel is then snapped into the other leg 22' of the block 22. The slides `III to I9 are then slit back, springs 32 facilitating theentrance of the wedges; II! into the recess of the block 22 between the opposite inner wings of the two U-"channels and the eccentrices I6 are simultaneously turned the desired angle so as to wedge the gang nut Ill against said wings and press the lower jaw II up against the bottom of the U-channels. l

, Thus anchored to the fixed part 22 of Vthemachine, the work sheet 20 can be stretched beyond its elastic limit and permanently deformed into the desired shape, by applying pressure fluid, thus being given a permanent deformation lwithout having to carefully control the pressure applied, aslthe upturned edges of `the sheet 20 will merely slip out of the clamp if this pressure reaches a value above the ultimate tensile strength of said sheet, instead of excessive stretching forces tearing the sheet, as was usually heretofore the case.

By having interchangeable blocks ZI, 22 of varying shapes and lengths, it is possible to use the machine for forming a great variety of shallow. skin-sections of aircraft structures, and vby interposing shims 33 between the upper heads` I3 of the studs I2 and the wedges I il, it becomes possible to' form sheets of different gage without having to malte any change or adjustment inthe machine. It is to be noted, that, as there is no vibration in the machine during its operation, the clamping assemblies I0 to I9 can be, and are,

self-locking. l l

After the sheet 2i) is thus stretched to the desired extent and formed, the `hydraulic pressure is released and the two opposed handles I9 are turned in order to loosen the clamp. The block 2l then falls from the operative position shown in Figure 3 into the inactive position shown ,in Figure 2, while the plates I I fall on the table 25, 25 and the wedges I8 are lifted by the actionof the springs 32, thereby freeing the sheety 23, which can then be easily removed endwise fromvthe gripping jaws, III, `II and 22. f

The retaining channels of the skin-section thus obtained may, after this removal, eitherbe trim-- med away, or be retained as reinforced edges,

which may later on, when yassembled with the usual transversal ribs and a longitudinal web riveted to the bottom of these channelsform the spar of an aircraft or'other structure, such as of a fin, flap or the like. Y

Although, in the disclosed embodiments'vthe clamping pressure is manually applied and is independent of the stretching or drawing 'mechanism, it is to be understood -thatthisrrelamping pressure can be applied by any other suitable means. n

It will be noted that the stretching machine is an internally expanding one and has a single, central clamp adapted to associate the two lower longitudinal edges of the sheet closely adjacent each other .in juxtaposition in such manner as to form thereby, a single continuous force-absorbing structure thereat, the forming-zone consisting of two internally separable blocks in juxtaposition with each other, over which the sheet-metal is stretched by internal expansion. The work thus substantially completed envelops the entire forming zone, in which zone the pressure acts by internal expansion. The expansion is achieved by automatic power means and the blocks form a compact form-unit which unit may be varied in size, at will, by interchanging with blocks of other sizes. VIn operation, the sheets form an oilseal between the otherwise separated blocks. Insertion of fresh work sheets is also facilitated and rendered easier than heretofore, by these means, and yet the original advantages of the foregoing machine are retained withal.

The foregoing describes in detail a stretch press found to be practical in carrying the ultimate forming of la, sheet 20 in accordance with the present method'. However it is to be understood that the structure shown and described is not essential perse to the practice of the present invention but is merely an example of the type of press or apparatus especially suitable to iinal forming of the sheet as taught by the instant method.

The present method consists in preforming the opposed edges of the sheet 2D to create a U-channel at each edge. Each of these channels comprises a flange 2B' formed substantially at right angles to the body of the sheet 20 carrying a terminal flange 2U spaced from the sheet 20 and at an acute angle to the flange 20. Thus the flange 2S rests over and slopes or converges toward the body of the sheet 20. Both of the U-channels are positioned or formed on the same side or face of the .sheet Z.

The creation of the U-channels, each consisting of the flanges 20' and 2li", is Vfollowed by a partial or rough preforming Aof the sheet 20 which may be'done either by engaging one U- channel over one of the legs 22 and then bending the body of the sheet 20 over the movable block 2I until the other channel maybe Vpositioned over the opposed leg 22', all as above described; or by bending the sheet 20 centrally between the channels until the latter rest substantially parallel and adjacent and facing one another, whereupon the sheet so roughly preformed may be slid over the block 2I with the legs 22' of the block 22 received in the adjoining channels. Whichever of these manipulations is` employed it is required that the sheet 20 be partially or roughly preformed so that the edge channels are adjoining and positioned Afor the reception .of the legs 22,' of the stationaryblock 22. When so preformed the flanges 2G' rest in approximately the same plane and the flanges 20" diverge.

The adjacent U-channels are then held against slippage and release by the application of clamping pressures transversely'of and normal to the ilangesrZIl and 20" thereof. Since the terminal flanges 2D" lie at acute angles to the flanges 2D' and converge on the preformed sheet 20 in opposite directions, the clamping pressure applied to each flange V2E!" results from a force directed at an angle to the direction of the force of the pressure applied to the coacting flange 20'. It

is to be understood that the clamping pressures f are applied to the entire flange 20' as well as to the entire ange 20 and that at the angles between the flanges 20' and 20".

A final forming and stretching of the sheet 2D is accomplished by the application of pressure within the roughly or partially preformed sheet 20 with its U-channels clampingly held as aforesaid. This final forming pressure is applied to the inner surface of the partially preformed sheet in a direction generally away from the clampingly held channels and in effect acts in all directions against -the inner surface of the sheet.

By positioning the engaged preformed edges of the sheet 20 in relatively close proximity and by applying the nal forming pressures internally of the partially formed sheet and generally in alignment with such engaged edgea'the ultimate shape of the formed body does not limit the use of the present method. Thus a body restricted at both ends or in other words a body centrally larger than at its ends may be readily formed by following the teachings of the present invention.

It has been found that kthe combined clamping f pressures exerted on each U-channel at the edges of the sheet 20 must always exceed the final form` ing pressure internally applied to the body of the sheet being stretched, formed and shaped and the clamping pressure on the terminal flange 20" of each channel must be and is always greater flat metal sheets consisting in forming openchannels along opposed edges of a sheet positioned upon the same side of the sheet, partially preforming the sheet by bending it medially of said channels whereby the latter rest inwardly of the sides of the preformed sheet and in close proximity one to the other, clampingly engaging said channels, and applying pressure against the inner surface of the preformed sheet with the internal channels thereof so engaged.

2. The method of forming hollow bodies'from flat metal sheets consisting in so forming open channels at opposed edges of a sheet that said channels project from and above the same surface of the sheet, roughly preforming said sheet by bending it medially of said channels to bring said channels into relatively close proximity one to the other Within the limits of the space defined by the bending of the sheet, applying a clamping and engaging pressure throughout the surfaces of said channels, and applying a final forming pressure to the inner surface of the sheet of less value than the total clamping and engaging pressure applied to each of its edge channels.

3. The method of forming hollow bodies from flat metal sheets consisting in bending the opposed edge portions of a sheet in the same direction to lie at approximate right angles to the body of the sheet, bending the outer edges of said edge portions inwardly at acute angles to create terminal lianges positioned over and converging toward the sheet, partially preforming the sheet by centrally bending it between its opposed edge portions so that the right angular edge portions rest substantially coplanar and the terminal lianges diverge one from the other, applying clamping pressures normal to each of the coplanar edge portions, applying a greater clamping pressure normal to each terminal flange, and completing the formation of the hollow body by applying a pressing and stretching pressure to the inner surface of the partially preformed sheet of less value than the sum of the values of the clamping pressures applied as raforesaid to the flanges. i

4. The method of forming a hollow body from a flat metal sheet consisting in angularly disposing opposed edge portions of the sheet in the same direction, creating terminal flanges on the angularly disposed edge portions by bending the outer extremities thereof toward the center ofthe sheet, partially preforming the sheet by bending it centrally to bring the opposed edge portions toward each other thereby locating the angularly bent edge portions and terminal anges thereof within the area defined by the preformed sheet with the angularly disposed edge portions in ap-proximately the same plane, clampingly engaging said edge portions and terminal flanges, and applying a stretching pressure against the inner' surface of the body of the sheet between the clampingly engaged portions thereof. l y

5. The method of forming a hollow body from a fiat metal sheet consisting in disposing opposed edge portions angularly to the sheet, partially preforming the sheet by bending it centrally to position said angularly bent edge portions in approximately the same plane within the area defined by the sheet so bent, clampingly engaging the 'angularly disposed edge portions, and applying a stretching pressure to the inner face of the sheet between said edge portions.

6. The method of forming a hollow body from a flat metal sheet consisting in disposing opposed edge portions angularly -to the sheet, vpartially preforming the sheet by bending it centrally to position said angularly bent edge portions in approximately the same plane within -the area defined by the sheet sorbent, clampingly engaging the angularly disposed edge portions from the interior of the hollow body roughly formed by said preforming, and applying a stretching pressure to the inner surface of the sheet between the clampingly engaged edge portions.

HOWARD M. JAGER. EDOUARD SCHENK. 

